Method of and apparatus for electrical communication



June 26, 1923.

D. G. M CAA METHOD OF AND APPARATUS FOR ELECTRICAL COMMUNICATIOH Filed Jan. 19 1920 R m m m 7 ATTORNEY.

Patented June 26, 1923,

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DAVID G. MCCAA, OF LANCASTER, PENNSYLVANIA, ASSIGNOR OF ONE-THIRD TO FEDERAL TELEGRAPH COMPANY, 'OF SAN FRANCISCO, CALIFORNIA, A CORPORA- TION or CALIFORNIA;

METHOD OF AND APPARATUS FOR'ELECTRIGAL COMMUNICATION.

Application filed January 19, 1920. Serial No. 352,463.

To all whom it may concern. Be it known that I, DAVID G. MoCAA, a citizen of the United Statesresiding in the city of Lancaster, county of Lancaster, State of Pennsylvania, have invented a new and useful Method of and Apparatus for Electrical Communication, of which thefollowing is a specification.

. My invention relates to a method of and apparatus for electrically communicating signals or intelligence, telegraphically, telephonically orotherwise, by recourse to high frequency waves which may be transmitted over a conductor system extending between stations or, and principally, which are converted into electro-radiant energy trans mitted through the natural media between stations.

It is the object of my invention to provide a method of and apparatus for electrical communication of the character referred to which shall render practically harmless or substantially eliminate the effect of-natu-.

ral electricity, as atmospheric disturbances, static, strays, damped waves from radio transmitters employing'spark gaps, or other interfering electrical effects.

In some of its aspects my invention is similar or contains features germane to my prior application Serial Number 342,355, filed December 4, 1919. a

For an illustration of some of the various forms my apparatus may take, and for an understanding of my method, reference is had to the accompanying drawings, in which F ig.-1 is a diagrammatic View of transmitting apparatus. i

Fig. 2 is a diagrammatic view of receiving apparatus.

Referring to Fig. 1, A represents generically any transmitting conductor, as an an tenna, of open circuit, loop, coil, or any other suitable type, or a line conductor (BX-1 tending to the receiving station.

Between the antenna and theea'rth E is connected'the variable loading or tuning in ductance L and the secondaryof'an oscillation transformer T, whose primary is inthe anode circuit of the thermionic or elecgrid 9, and incandescent cathode or filament f, the latter supplied with current from battery I) and whose strength is regulated by resistance r. In the anode circuit is the battery B, which may be shunted by the condenser C, and a coupling coil L in inductive relation with the coil L in the grid circuit, an adjustable condenser C be ing associated with the parts described for causing production of oscillations of any desiredfrequency, for example, radio frequency, and for purposes of illustration may be assumed to be 200,000 per second. A secon-delectronic or thermionic oscillator V has in its anode circuit the battery B which may be shunted by the condenser G a telegraphic key k, the coupling coils L 'and L. variable condenser C and the primary of the oscillation transformer T whose secondary is the oscillator V, a variable tuning condenser C being connected in parallel withthe seco'ndary of the transformer T The oscillator V oscillations of frequency above audibility, for example, 20,000 per second. When the signaling key Z. is closed, the potential of the grid 9 of oscillator V is accordingly periodically varied at 20,000 per second, wherebythere is impressed upon the transmitting medium by transformer T oscillations of a frequency of 200,000 per second varying in amplitude at modulator frequency, to wit, 20,000 per second.

For purposes of telephony, the key in may he keptpermanently closed and the switch .5 closed, whereby the microphone m, in circuit with the battery 6 and the primary of a transformer T may cause the secondary of that transformer, which may be shunted by the variable tuning condenser C to vary the potential of the grid 9 'of the modulator oscillator V in accordance with speech. The result is that the transformer T impress'esupon' the transmitting medium oscillations of 200,000 frequency varying in amplitudeat modulator frequency, 20,000 per second, and varying in amplitude also in acin the circuit of the grid 9 of produces modulating able type including those hereinbefore referred to, or a line conductor extending from the transmitting station. When it is an antenna or the like, its path may be tuned by the inductance L between which and earth E is connected the primary of the oscillation transformer T The antenna path is preferably tuned to the frequency of the energy transmitted, for example, 200,000 per second. The secondary circuit of the transformer T is also preferably tuned to the same frequency. as by tuning inductance L and capacity C, associated with the grid. circuit of the thermionic or electronic detector V in whose anode circuit is the battery B and the primary of the transformer T", current Waves of modulator frequency, 20,000 per second, being produced in the primary and secondary of the transformer T In the secondary circuit are connected the primaries. P and P so wound or connected that they both produce at their right ends, at agiven instant, thesame polarity, for example, south poles. Inductively related with these primaries, respectively, are the secondaries S and S with which are connected,,respectively, the grids g and g of thermionicdevices whose electrodes may be in the same .or different evacuated tubes. In the example illustrated, the thermionic device V has a single vacuum containing the aforesaid grids, with which are associated, respectively, the anodes a and al with ,a common filament f whose one terminal is connected through both the secondaries S and S In the anode circuits are connected the battery B and the primaries P and P of a transformer T these primaries being opposed to each other in their inductive effeet upon the secondary S in circuit with which is connected the telephone Pk.

Also inductively coupled with the transformers S and S respectively, are the coils 1 and P so wound or connected that at the same instant they exhibit at their left ends different polarities. These .coilsare in the circuitof the grid 9' of the thermionic oscillator V in whose anode circuit is the battery 13*, which may be shunted by the condenser C and the coupling coils L and L a variable tuning condenser C being connected across the grid and filament. The operation is as follows: WVith the transmitter impressing upon the medium intervening between the transmitting and receiving stations undam-ped waves, varying in amplitude at frequency above audibility, there are produced in the secondaries S and S currents of modulator frequency, for example, 20,000 per second; but they simultaneously similarly affect the grids g and 9 so that like currents simultaneously traverse the primaries P and P which, since they are differential in their action, produce no inductive effect upon the secondary S and nothing is heard in the telephone Pit, unless the oscillator V is in operation producing oscillations of a fre quency of 21,000 per second, for example, whereby there are produced in the circuits of the grids g and g of the thermionic de vice V beats of audible frequency, 1,000 per second, but dephased with respect to each other by practically 180 degrees, causing in the primaries P and P currents dephased substantially 180 degrees, which, however, because of the differential winding or connection of'the primaries P and P, cumulatively affect the secondary S producing in the telephone Ph an audible note having a frequency of 1,000 per second, which n'ote appears for long and short periods according to the length of time the key 72 at the transmitter is depressed to form dots and dashes.

Or for telephony, with the key is closed, switch 8 closed and the microphone m spoken into, there will be transmitted, as stated, undamped waves modulated in amplitudeat modulator frequency, as 20,000 per second, and varying in amplitude also in accordance with speech.

At the receiver, for telephony, the oscillator V will be set to produce current of such frequency that the beats produced in reaction in the secondary coils SP and S with the modulator frequency of 20,000 per second, will be above audibility. In such case, the beats operate cumulatively upon the secondary S but being inaudible, will produce no effect in the telephone Ph; but the envelope of these inaudible beats represents speech, which will be reproduced by the tele phone P72.

In the case of both telephony and telegraphy, or other mode of signaling by the method and apparatus described, the effects of static, natural electricity, strays, or damped waves from transmitting apparatus employing a spark gap, will have no dis-- turbing or interfering effect upon the transmission of the signals "or messages for the rea sons explained in my aforesaid application Serial Number 342,355; that is, because the interfering effects balance out as to the secondary S because of the di-fierential effects of the primaries P and P for all simple de: tector effects, as distinguished from heat effects caused by the tube 13":

By modulating the transmitted energy whereby it comprises und-amped waves varying in amplitude at predetermined frequency above audibility, thepossibility 'of interfe'n ence by natural atmospheric effects or other transmitting stat-ions, especially when radiating damped waves, is further reduced, because the disturbing impulses or effects cannot produce substantial effects of modulator frequency, for example, 20,000 per second, and "such effects. as are so produced are prejoint effect upon a translating instrument enact f m att s i g v e h e by t e tingintelligence, which consists in producing high frequency oscillations,modulating: the amplitude thereof at a constant frequency above audibility, controlling the same to represent the intelligence to be transmitted, impressing the energy upon a transmitting medium, receiving the energy from said transmitting medium and eflecting thereby current of said constant modulation frequency, impressing said current upon different paths Whose joint effect upon a translating instrument is substantially nil, causing to react with said current locally produced current waves of frequency producing equal and opposite beats of com stant frequency, and causing said beats to affect said signal translating instrument cumulatively.

2. The method of electrically transmitting intelligence, which consists in producing high frequency oscillations, modulating the amplitude thereof at a constant frequency above audibility, controlling the same to represent the intelligence to be transmitted, impressing the energy upon a transmitting medium, receiving the, energy from said transmitting medium and effecting thereby current of said modulation frequency, impressing said current upon dif ferent paths whose joint effect upon a translating instrument is substantially nil, causing to duced varying in amplitude at a constant frequency above audibility, which consists in effecting by the received energy current of said second named frequency, impressing said current upo-n difierent paths whose joint effect upon a translating instrument is substantially nil, causing to react with said current locally produced current of different frequency to produce substantially equal and opposite beats of constant frequency, and causing said beats to affect said signal translating means cumulatively.

4. The method of receiving intelligence represented by l waves of radio frequency varying in amplitude at a constant frequency above audibility, which consists 111 eflecting by the received energy current of said second named frequency, impressing said current upon different paths whose is substantially nil, causing to; react with said current locally produced current of means for effecting by the react with said current locally pro current waves of frequency produc ing equal and opposite audible beats of concurrent of said current, detector circuits different frequency to produce equal and opposite beats of constantaudible frequency, and causing said beats to afi'ect saidsignal translating means cumulatively.

,5. system for electrically transmitting substantially intelligence comprising means forproduc ing .high frequency oscillations, means for varying the amplitude of said oscillations at predetermined frequency above audibility, means for controlling the energy in accordance with the intelligence to be transmitted, and receiving app ratus comprising received energy current of said predetermined frequency, a signal translating instrument, means for rendering the direct effect of said current upon" said instrument substantially nil, means for producing oscillations of a frequency' different fromsaid predetermined frequency, means causing said oscillations to react with said current to produce substantially equal and opposite beats of constant frequency, andmeans for subjecting said translating tive effects of said beats.

6. Apparatus for receiving intelligence represented by high frequency energy vary ing in amplitude at predetermined frequency, comprising a rectifier producing current of saidjpredetermined frequency, a plurality of paths inductively affected by said current, a signal translating instrument differentially affected by said paths,

means for producing oscillations different from the frequency of said current, means instrument to the cumulapaths by said oscillations whereby equal and opposite beats of constant frequency are produced in said paths, said beats cumula tively affecting said translating instrument.

7. Apparatus for receiving intelligence represented by high frequencv energy varying in amplitude at predetermined frequency, comprising a receiving conductor, means associated therewith for effecting a predetermined frequency, transformer primaries traversed by said coupled with said primaries, opposing windings associated, respectively, with said detector circuits, a source of oscillations oppositely coupled with said detector circuits and reacting with the current therein to produce substantially equal and oppositely beats of constant frequency, whereby said opposing windings operate cumulatively respecting energy.

8. Apparatus for receiving intelligence represented by high frequency energy varying in amplitude at predetermined frequency, comprising a receiving conductor, means associatedtherewith for effecting a current of said predetermined frequency, transformer primaries traversed by said current, detector circuits coupledwith said the beat l the current therein to produce substantially equal and opposite beats of'constant frequency. a

In testimony whereof I have hereunto affixed my signature this 16" day of January, 1920. V DAVID G. MCCAA, 

